This invention relates to a gas turbine jet engine of the type with a fan delivering into a bypass duct to generate mainly propulsion thrust, and with a thrust reversing device having flaps which for reverse thrust operation pivot into the fan air stream and cooperate with an axially extended movable extreme section of outer wall of the bypass duct to uncover deflection ports at breakthroughs in the outer wall. The invention particularly embraces aircraft engines in the modern propfan category with a shrouded blower or fan, where a fan air stream of extremely high bypass ratio of about 8:1 to 20:1 and over, generating the main propulsion thrust, is delivered into a bypass duct of varying length, depending on the type of engine involved, which envelopes the basic engine.
With a view to variable flight conditions, more particularly cruise flight operation, take-off phase, climb phase and deceleration processes (reverse thrust mode), the need to optimally adapt the engine from control and aerodynamic aspects to suit the associated variable thrust and performance requirements often involves considerable high-cost or uneconomical engineering penalties.
To be able to operate the engine over the entire operating regime with a comfortable margin relative to the surge limit (i.e. without compressor surge), the practice has been in prior art to prevent surge phenomena in configurations employing fixed and constant nozzle areas for the fan delivering into the secondary cycle or bypass duct by effecting relatively minor variations in blade pitch, sometimes in combination with extremely high torsional deflection of the fan blades, as in the full reverse thrust mode when air is being ingested from the rear. With priorart propfan engines having counterrotating fan blades on different rotors, this requires high-precision, elaborate individual blade actuating bearing provisions on the respective rotors, plus the associated variable-control blade actuating means.
Another difficult-to-surmount engineering problem involved is that of the mechanical loads the fan blades must undergo when operating in the reverse thrust mode.
In order to alleviate the engineering and control effort for variable fan blades with a view to variable engine load conditions, it has specifically been proposed to make the fan blades nonvariable and eliminate the risk of compressor surge by configuring the respective end of the outer fan wall or bypass duct partially as flaps which in thickness correspond to the outer wall and which serve to enlarge the fan nozzle area by flaring the flaps to suit the requirement for augmented mass flow and thrust (e.g. take-off or climb phase vs. cruise flight); and it has also been proposed to deploy the same flaps past the cruise flight nozzle position and into the fan propulsion jet for thrust reversing action while locally uncovering and forming thrust reversing ports at the aft end. In the interest of but a single respective flap pivot, said proposed arrangement would only in the cruise position achieve a reasonably streamlined outer contour of the shroud end in its segmented flap arrangement, and the requirement for maintaining a widened nozzle area when reverse thrust operation commences (deploying past the cruise nozzle position from the widened nozzle position) to provide the augmented mass flow to meet the higher thrust requirement is not satisfied. Also, the proposed arrangement involves relatively thick-walled, heavy-weight flaps and, hence, greater actuating forces to move them.
Disclosed in German Published Unexamined Patent Application (DE-OS) 20 18 967 is a thrust reversing arrangement for the fan air stream of a gas turbine jet engine, where jet deflection cascades axially protecting from an upstream portion of the outer bypass duct wall are uncovered on both sides by axially displacing a shroud end enveloping the cascades in the cruise position, and where thrust reverser flaps hinged to the centerbody are simultaneously deployed into the fan air stream; so that the thrust reverser flaps, when in the cruise position, form a partial section of the bypass duct inner wall on the upstream side of the cascades. Using said deflecting cascades, then, the respective thrust reverser flaps are merely shut-off means and aids to deflect the fan air stream towards the cascades. In this arrangement the movable extreme portion containing the outer annular nozzle shroud is a heavy-weight component necessitating relatively great actuating forces.
Nor does this prior art provide tangible approaches whatsoever to increasing the thrust nozzle area in critical load cases (takeoff phase, climb phase, reverse thrust operation) or to reducing the engineering and control effort especially with a view to modern propfan engine concepts of extremely high bypass ratios. This also applies in conjunction with a thrust reversing arrangement disclosed in German Published Unexamined Patent Application (DE-OS) 1 930 829 for the fan air stream of a ducted fan engine, where breakthroughs formed and locally staged between fixed, thick-walled wall portions of an outer fan stream shroud are covered flush or uncovered by pivotally arranged thrust reversing flaps designed to suit the breakthrough contours on both the inside and the outside such that these flaps can extend into the uncovered breakthroughs and form the major thrust deflection aids.
In a broad aspect the present invention provides a gas turbine jet engine of the generic description offered above, where engine load conditions departing from the cruise phase (e.g. take-off phase, climb phase, reverse thrust operation) can favorably be handled aerodynamically as regards the outside air and fan air streams, at comparatively moderate control and actuating efforts.
According to preferred embodiments of the invention, an arrangement is provided wherein the extreme movable section of the outer wall and the thrust reverser flaps are linked one with the other for relative movement between them such that in a first phase of actuation relative to a fixed extreme nozzle section of the bypass duct, the movable extreme section provides an additional fan nozzle area which communicates with inlet flow areas uncovered by the flaps relative to the bypass duct.
The present invention accordingly provides a technically comparatively simple arrangement for diverting a fan air stream portion from the secondary cycle through inlet flow areas uncovered upstream by the thrust reverser flaps (dipping movement into the bypass duct) and ducting it to the additional nozzle or nozzle area; so that the subsequent diverting process continues through the breakthroughs, between the axially movable outer extreme section and the thrust reverser flaps; and where especially in the first actuating or engine load control phase, a streamlined uninterrupted outer contour of the duct wall (small outer wall contour tail angle) is ensured over the distance from the upstream wall of the breakthroughs to the fixed nozzle section; and except for the deliberate opening of the inlet flow areas in the bypass duct, the fan air stream is--throughout the first actuating phase routed in practically the absence of aerodynamic turbulence or disturbance inside and downstream of the inner wall of the fixed nozzle section, to the primary annular nozzle area of the fan bypass duct provided by the said fixed nozzle section.
By means of the multipoint actuating kinematics of especially preferred embodiments to be discussed more fully below, plus the associated design and arrangement of the tracks, the thrust reverser flaps, being substantially longer axially than the breakthroughs, can be pivoted in a further parabolic lift/thrust movement (i.e. in the second actuating phase) locally through the breakthroughs so that in the reverse thrust position they project relatively far from the breakthroughs and simultaneously form the deflecting aids to guide the deflection stream while obviating the need for deflection cascades or similar devices. Thus, the arrangement of the present invention accordingly provides the nozzle exit area generally needed for thrust reversing operation between the respective extreme sections of the wall at the breakthroughs, these sections arching diagonally upwards from the inside to the outside, and the upstream sections of the flaps deployed into the breakthroughs, these latter sections acting as spoilers in the ambient air stream. Even when fully extended axially in the full reverse thrust position the extreme section produces no appreciable additional aerodynamic disturbance in the outside air stream.
The arrangement of the present invention provides another advantage by enabling a noncritical (for the engine) load transition from the first to the second actuating phase (additional nozzle area/thrust reversal) to be achieved by making the additional nozzle area provided in the first phase available already at the time the thrust reversing phase commences, so eliminating the need for newly creating it by means, e.g., of extra actuating kinematics. In all positions of the axially movable extreme section and the correspondingly variable thrust reverser flaps, then, the engine fan is given the total propulsive nozzle area it needs to cope with the engine load at the moment.
Without first having to operate the thrust reverser at all, therefore, the combination of movable extreme wall section (additional nozzle area) and flap actuation (uncovering the additional inlet flow areas leading to the open additional nozzle) provides in the first actuating phase, the vital means to cope with critical load cases deviating from the cruise phase (e.g. take-off phase, climb phase) such that compressor surge is prevented.
In a further advantageous aspect of the present invention the actuating elements plus associated control means of the actuating kinematics to be described below produce no aerodynamic disturbance in the outside air and the inner fan or bypass stream; the actuating elements and the tracks to be described more fully below can advantageously be arranged in, e.g., spaces between lands extending along the breakthroughs. Flap actuating levers, which are the only elements continuously extending into the fan air stream, can--to alleviate their drag--advantageously be arranged in the aerodynamic wake areas of struts extending for constructional and strength reasons between the outer wall and the centerbody of the engine, where the centerbody can simultaneously form the inner wall of the bypass duct.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.